GA(3) APPLICATION ALTERS FLOWERING PHENOLOGY OF HASS AVOCADO

The objectives of the present research were to quantify 1) the contrib ution that vegetative shoots produced in the summer vs. fall and indet erminate vs. determinate inflorescences make to yield and 2) the effec ts of GA(3) on flowering expression and inflorescence phenology of sum mer and fall shoots of 'Hass' avocado (Persea americana Mill.) under f ield conditions. Anthesis started earlier on fall than summer shoots o f 10-year-old 'Hass' avocado trees; however, no difference in the date of full bloom was observed. Indeterminate inflorescences that underwe nt early anthesis set more fruit than those with delayed anthesis, con versely, determinate inflorescences with delayed anthesis set more fru it. Indeterminate inflorescences comprised 90% of total inflorescences and contributed 73% of total fruit yield, but individual determinate inflorescences were at least three times more productive than the inde terminate ones. Summer and fall shoots were sprayed with 0, 50, 100, o r 1000 mg.L-1 GA(3) in November, December or January. GA(3) stimulated apical growth of all shoots. If secondary axes of an inflorescence bu d were differentiated at the time of GA(3) application, the infloresce nce developed in advance of inflorescences on branches not treated wit h GA(3), In addition, GA(3) caused precocious development of the veget ative shoot of indeterminate inflorescences relative to the flowers in the same inflorescence and relative to the vegetative shoot of indete rminate inflorescences from untreated branches. Stimulation of vegetat ive growth at the inflorescence apex by GA(3) inhibited growth of axil lary buds. GA(3) at 50 mg.L-1 had no effect on the number of determina te or indeterminate inflorescences produced by either summer or fall s hoots. Higher concentrations of GA(3) increased the number of vegetati ve shoots and inactive buds produced by both shoot types.